Japanese Laid-Open Patent Application No. 1-224929/1989 (tokukaihei 1-224929) suggests and discusses in detail a configuration in which a groove functioning as a servo track wobbles in radial directions of the disk in order to increase the recording capacity of a recordable optical disk. FIG. 21 illustrates an example of such a configuration. A groove 201 functioning as a servo track (shown in FIG. 21 as the areas with slanting lines) is provided by the constant linear velocity method in advance so as to wobble in radial directions of the disk 200 (the directions R in FIG. 21) in accordance with address information modulated with respect to frequency. That address information is hereinafter referred to as the prerecorded address information.
A frequency band between the information-recording band and the tracking servo band is allocated as the wobbling frequencies, i.e., the frequency band of the prerecorded address information. For example, a format used in CDs (Compact Discs) and CD-ROMs (Compact Disc-Read Only Memories) employs a center frequency of 22.05 kHz, or about 1/10 of the lower-limit frequency of the recording information, for prerecorded address information signals. This is because the center frequency is capable of restraining affection of the recording information on the signal quality.
In a disk recording and reproducing device, the prerecorded address information is extracted from error signals obtained through tracking of the groove functioning as a servo track. Then the rotation of the disk is controlled so that the center frequency of the extracted address information equals 22.05 kHz. The rotation of a disk is thus controlled by the CLV (Constant Linear Velocity) method. In addition, the address data is obtained by demodulating the prerecorded address information. It is, in this way, possible to carry out access operation to any position over the disk, including an unrecorded area of the disk, and recording and reproduction operation. Since the linear recording density can be made constant in any part of the disk in this way, the recording capacity of such a disk is greater than conventional disks employing the CAV (Constant Angler Velocity) method.
FIG. 20 illustrates a sector allocation used in a disk when the above configuration is applied to a CD. (17a) represents an information sequence composing the prerecorded address information obtained from the groove wobbling in radial directions of the disk, (17b) represents an address allocation of the prerecorded address information in the groove, (17c) represents sectors allocated for the recording information recorded in the groove, (17d) represents an information sequence composing the sectors, and (17e) represents an information sequence composing the sub-code address information in the sectors above. The prerecorded address information is, as shown in (17a), composed of an SYNC (denoted as "a1" in FIG. 21) representing the beginning of each piece of the address information, first address data a2 representing the real address value, and a CRC (denoted as "a3" in FIG. 21), that is, a code for detecting errors in the first address data. These components of the prerecorded address information form a block as corresponding physical areas. The prerecorded address information is provided on the entire disk surface as a continuous tracking groove which wobbles in radial directions of the disk as shown in FIG. 21. Therefore, the continuous wobbling groove has, as shown in (17b), a block b1 which corresponds to a block address Pa1, a block b2 which corresponds to a block address Pa2, and so on.
Meanwhile, the recording information recorded in the groove is divided into sectors c1, c2, and so on as shown in (17c). A sector address Ga1 is allocated to the sector c1, a sector address Ga2 is allocated to the sector c2, and so on. The sector c1 corresponds to the area of the block b1, while the sector c2 corresponds to the area of the block b2. Therefore, the sector address Ga1 corresponds to the block address Pa1, while the sector address Ga2 corresponds to the block address Pa2 (Here, the "block" has the same meaning with the "sector"). As shown in (17d), an EFM (Eight to Fourteen Modulation) frame is composed of a synchronous field d1 which represents the beginning of the recording information, a sub-code field d2 which includes sub-code address information, and a data field d3 in which the recording information, error detection correction codes and the like are recorded. Ninety eight of such frames, in turn, compose each sector above. The 98 sub-code segments, taken out and connected, form sub-code address information which is composed of a synchronous field e1 which represents the beginning of the recording information, a sub-code address field e2, and a CRC field e3 for detecting errors in the sub-code address.
Here, the physical area of the above block equals the physical area of the sector. Therefore, the value of the prerecorded address equals the value of the sub-code address. Generally, the smallest unit for recording and reproduction of user data is a group called a sector. Nevertheless, in the disk having the above configuration, (1) a unit where the prerecorded address information (17a) is given is allocated as a sector, (2) the prerecorded address information is used as a sector number, and (3) the recording information (17d) which includes the same address value corresponding to that prerecorded address information in the form of the sub-code is located in that sector.
Japanese Laid-Open Patent Application No. 5-314538/1993 (tokukaihei 5-314538) suggests and discusses in detail a configuration in which only one of the side-walls of a groove functioning as a servo track wobbles in radial directions of the disk in order to increase the track density of an optical disk. As shown in FIG. 22, prerecorded address information is provided in advance in a disk 210 as a wobbling groove 211 (shown in FIG. 22 as the areas with slanting lines). Only one of the side-walls of the groove 211 wobbles. The groove 211 and the land 212 between adjacent parts of the groove 211 have about the same width. For these reasons, it is possible to detect address information from the groove 211 and the land 212, and to record information into the groove 211 and the land 212. The track density is thus increased.
Nevertheless, in both configurations above, since the address information is prerecorded in the wobbled configuration (an irreversible state), the sector sizes are fixed for each disk. This does not matter if the sector sizes are enough small. If the sector sizes are great, however, this causes not only a decrease in the data utilization factor but also an increase in the process time needed for recording and reproduction of data. More specifically, for example: Even when data of 500 bytes is to be recorded, one sector is still allocated for the recording. So, if the sector size is 2048 bytes and 4096 bytes, the utilization factor will be about 25% and 12.5% respectively. Moreover, the time necessary for the data to be recorded will be 4 times and 8 times respectively. An alternative way is small sectors. But, in the above case where the prerecorded address information is employed in a CD-ROM format, a sector size of 2048 bytes is set. If this is adopted with smaller sector size of 1024 bytes and 512 bytes which are used in, for example, ordinary computers, the wobbling frequency will double and quadruple, nearing the frequency band for the recording information. Therefore, the prerecorded address information cannot be adopted in formats of small sector sizes.
Moreover, it is possible to know from an error detection bits if the address data of prerecorded address information in a disk having the above configuration is correct or false. The address data, however, does not have error correction function and is not capable of performing recording and reproduction with high reliability. Some of the solutions for this problem are: adding error detection bits to prerecorded address information, and multiple recording address data. These solutions are, however, can not avoid increasing the number of bits allocated for the prerecorded address information, thereby raising the wobbling frequency of the prerecorded address information, interfering the frequency band for the recording information, and affecting signal quality of the recording information. Furthermore, the prerecorded address information is extracted by a detection system of a tracking servo. Therefore, the higher frequency band of the prerecorded address information results in a higher frequency band required by the tracking servo detection system, which leads to another problem.